Soaking up metals improves carbon capture

23 April 2018
| David Bradley

Amine-based adsorbents that can soak up carbon dioxide have been made fifty times more stable thanks to efforts by Minkee Choi from the Department of Chemical and Biomolecular Engineering at KAIST, the Korea Advanced Institute of Science and Technology. The novel materials are much more resistant to oxidative damage than their predecessors and could take us a step closer to a tenable CO2-trapping system for combating the effects of rising atmospheric concentrations of this greenhouse gas on global warming and climate change.

Choi and graduate student Woosung Choi, and colleagues Kyungmin Min and Chaehoon Kim describe details in the journal Nature Communications. While carbon capture as a means of combating climate change has been a research topic for many years, science and technology have struggled to find a viable solution. However, one promising lead is represented by amine-containing adsorbents that are efficient at soaking up the gas and themselves are environmentally benign. Unfortunately, the amine adsorbents developed so far have been found to be unstable to atmospheric oxidation and break down chemically within relatively short periods of time. This makes it almost impossible to rely on this class of materials as it stands as adsorbents for repeated and continued use. [Choi et al, Nature Commun (2018) 9, No. 726; DOI: 10.1038/s41467-018-03123-0]

The KAIST researchers have now discovered that tiny contaminants in the form of iron and copper ions in the materials can catalyze this oxidative breakdown. With this knowledge in hand, the team has now proposed the use of chelating agents to mop up the metal contaminants and so suppress the catalytic oxidation. In a belt and braces approach, the team has also functionalized their polyethyleneimine (PEI) adsorbent with 1,2-epoxybutane, which they explain generates tethered 2-hydroxybutyl groups.

The researchers have now demonstrated that they can reduce instability due to oxidation by some fifty times when compared to the standard PEI adsorbents supported on a silica substrate with this functionalization and the addition of the chelating agents to the substrate. In proof-of-principle experiments the team has shown that their adsorbent with added chelating agent performs far better than standard materials and its ability to capture carbon dioxide falls by only a small percentage due to oxidative degradation. The conventional adsorbent without chelating agent is deactivated dramatically after being exposed to oxidative aging within just thirty days. Indeed, rather than it being belt and braces, the use of the two stabilizing effects works synergistically in improving the stability of the adsorbents, the team says.

The team suggests that this stability improvement could ultimately make the materials commercially viable. First author on the research paper Woosung Choi describes the significance of the work as, "having brought solid carbon dioxide adsorbents to commercializable standards." Choi adds that the team is indeed already working towards commercialization and hopes to "develop the world's best carbon dioxide capture adsorbent."

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".

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